The Highly Dynamic Behavior of the Innermost Dust and Gas in the Transition Disk Variable LRLL 31

TL;DR

This study presents extensive multi-wavelength observations of the transition disk LRLL 31, revealing rapid variability in the inner disk's dust and gas, likely caused by a companion beyond 0.4 AU or magnetic interactions, rather than accretion or wind effects.

Contribution

The paper provides detailed multi-epoch observational data of LRLL 31, constraining the physical mechanisms behind its rapid inner disk variability and ruling out certain causes like accretion and wind fluctuations.

Findings

Inner disk dust remains at sublimation radius with variable infrared excess.

Accretion rate varies by a factor of five, correlating with infrared excess.

No evidence of a close-in companion within 0.4 AU causing periodic variability.

Abstract

We describe extensive synoptic multi-wavelength observations of the transition disk LRLL 31 in the young cluster IC 348. We combined four epochs of IRS spectra, nine epochs of MIPS photometry, seven epochs of cold-mission IRAC photometry and 36 epochs of warm mission IRAC photometry along with multi-epoch near-infrared spectra, optical spectra and polarimetry to explore the nature of the rapid variability of this object. We find that the inner disk, as traced by the 2-5micron excess stays at the dust sublimation radius while the strength of the excess changes by a factor of 8 on weekly timescales, and the 3.6 and 4.5micron photometry shows a drop of 0.35 magnitudes in one week followed by a slow 0.5 magnitude increase over the next three weeks. The accretion rate, as measured by PaBeta and BrGamma emission lines, varies by a factor of five with evidence for a correlation between the accretion rate and the infrared excess. While the gas and dust in the inner disk are fluctuating the central star stays relatively static. Our observations allow us to put constraints on the physical mechanism responsible for the variability. The variabile accretion, and wind, are unlikely to be causes of the variability, but both are effects of the same physical process that disturbs the disk. The lack of periodicity in our infrared monitoring indicates that it is unlikely that there is a companion within ~0.4 AU that is perturbing the disk. The most likely explanation is either a companion beyond ~0.4 AU or a dynamic interface between the stellar magnetic field and the disk leading to a variable scale height and/or warping of the inner disk.